Strip-line circulator having movable compensating stub strip overlying central strip-line conductors

ABSTRACT

1. In a strip-line microwave circulator comprising at least three central strip conductors disposed between parallel outer conductors and connected at one of their ends at a central point with said strip conductors, being parallel to said outer conductors and extending radially outwardly from said point, including predetermined angles with each other, a pair of concentric gyromagnetic discs disposed at said point each between one side of said strip conductors and the adjacent outer conductors, and means to magnetize said discs in a direction substantially at right angle to said conductors, to create microwave circulators switching action; the improvement consisting in the provision of unitary stub conductors disposed between any two adjacent ones of said strip conductors, each of said stub conductors having one end coupled with the junction between the respective strip conductors and extending outwardly along the symmetry line thereof to a distance being in excess of half the radius and less than the full radius of said discs, said strip conductors being in the form of an integral Y-shaped conducting spider strip with the axes thereof including equal angles of 120* between them, said stubs consisting of a further spider strip concentric with and overlying said first spider strip and movable in a parallel plane relative to the latter so as to compensate for any minor imbalance of admittances at the input terminals of the circulator, said outer conductors comprising a first cover member and a bottom member extending over the respective ferrite discs, a casing ring connecting the first cover member to the bottom member, said means to magnetize said discs consisting of a single permanent magnet extending over said first cover member, a second cover member extending over said permanent magnet, the first and second cover members, a substantial portion of the casing ring and the bottom member being formed of magnetic material to provide a magnetic circuit for said permanent material.

United States Patent [451 Mar. 21, 1972 Ito et al.

[54] STRIP-LINE CIRCULATOR HAVING MOVABLE COMPENSATING' STUB STRIPOVERLYING CENTRAL STRIP- LINE CONDUCTORS [72] Inventors: Yukio Ito;I-Iaruo Yokouchi;'Ke 1ji Konno,

all of Kawasaki-shi, Japan [73] Assignee: Fujitsu Limited, Kawasaki-shi,Kanagawaken, Japan [22] Filed: Sept. 30, 1965 211 Appl. No.2 491,676

[30] Foreign Application Priority Data Oct. 6, 1964 Japan ..39/57000[52] U.S.Cl ..333/1.l, 333/9 [58] FieldofSearch ..333/l.l,9, 84M

[56] References Cited UNITED STATES PATENTS 3,359,510 12/1967 Geiszler..333/l.1

3,174,116 3/1965 Sur ..333/1.l

2,903,695 9/1959 Jamieson.. ..333/84 X 3,063,024 11/1962 Davis, Jr..333/1.l

3,165,711 1/1965 Drumheller et al ....333/l.1

3,185,941 5/1965 Freiberg ..333/1.l

Primary ExaminerHerman Karl Saalbach Assistant Examiner Paul L. GenslerAttorney-Greene & Durr EXEMPLARY CLAIM 1. in a strip-line microwavecirculator comprising at least three central strip conductors disposedbetween parallel outer conductors and connected at one of their ends ata central point with said strip conductors, being parallel to said outerconductors and extending radially outwardly from said point, includingpredetermined angles with each other, a pair of concentric gyromagneticdiscs disposed at said point each between one side of saidstripconductors and the adjacent outer conductors, and means to magnetizesaid discs in a direction substantially at right angle to saidconductors, to create microwave circulators switching action; theimprovement consisting in the provision of unitary stub conductorsdisposed between any two adjacent ones of said strip conductors, each ofsaid stub conductors having one end coupled with the junction betweenthe respective strip conductors and extending outwardly along thesymmetry line thereof to a distance being in excess of half the radiusand less than the full radius of said discs, said strip conductors beingin the form of an integral Y-shaped conducting spider strip with theaxes thereof including equal angles of 120 between them, said stubsconsisting of a further spider strip concentric with and overlying saidfirst spider strip and movable in a parallel plane relative to thelatter so as to compensate for any minor imbalance of admittances at theinput terminals of the circulator, said outer conductors comprising afirst cover member and a bottom member extending over the respectiveferrite discs, a casing ring connecting the first cover member to thebottom member, said means to magnetize said discs consisting of a singlepermanent magnet extending over said first cover member, a second covermember extending over said permanent magnet, the first and second covermembers, a substantial portion of the casing ring and the bottom memberbeing formed of magnetic material to provide a magnetic circuit for saidpermanent material.

2 Claims, 13 Drawing Figures QQOMPENSAT- mo STUB PATENTEDMARZI m2 SHEET1 OF 3 T R A R m R P IHVILM'TOR YUKIQ ITO ET AL KM/ Km PATENTEDMARZII972 3,651,430

sum 2 OF 3 DECOUPLING AMOUNTS 9 f "'10" I. 1.2 N O FREQUENCY TO MEANFREQUENCY RATIO OF WORKI [NW-.1 ."mR. YUKIO ITO ET AL W f g PATENTEDMAR21 I972 SHEET 3 BF 3 PERMANENT MAGNET 1/ 1/ 11/11 IIIIIIIIII v hah T 2 &

INVENTOR. YUKIO ITO ET AL STRIP-LINE CIRCULATOR HAVING MOVABLECOMPENSATING STUB STRIP OVERLYING CENTRAL STRIP-LINE CONDUCTORS Thisinvention relatesto broad band strip-line circulators which are recentlyemployed in the microwave technique, especially three-terminalcirculators comprising inner gyromagnetic members.

As well known to those skilled in the art, coaxial transmission linessuch as called strip lines" for transmission of high frequency electricwaves are provided with branching points, especially in the form of a Yor T, generally called strip circulators, each of which comprisesgyromagnetic members and is fitted with one or more magnetic bodieshaving amagnetic field perpendicular to said members. The width of theworking frequency band of this kind of circulator depends substantiallyupon the sizes and the kind and nature of the gyromagnetic material, andspecific dimensions of the transmission line.

Various attempts have been made to broaden the said working frequencyband by selecting a proper combination of these parameters. Furtherattempts have also been made to provide a parallel or series resonancecircuit in the extension of the circulator zone of the transmission lineso as to suppress to a certain degree the frequency characteristics ofoverall impedance or admittance as provided by the gyromagnetic membersin combination with the line material, thereby to improve inputimpedance, as well as the frequency characteristic of forward andreverse losses.

In the conventional broad band matching arrangement of the kind abovereferred to, parallel or series resonance circuit is additionallyprovided. According to the conventional This three-terminal circulatoris provided with a thin metallic sheet conductor 11 having threeradially extending arms as shown, each free outward end of whichconstitutes a terminal to be connected through a conventional connectorwith a high frequency wave transmission line, not shown. Ferrite discs12 and 13 are provided to make physical contact with the respectivesurfaces of the conductor 11 so as to cover a respective concentric zonewith a center which is constituted by a crossing point of thelongitudinal axes of the three arms. In the same manner as will be morefully described with reference to FIGS. l'and 11, a permanent magneticdisc is placed upon the upper surface of the upper ferrite disclZ so asto establish a unidirectional magnetic field directing in the verticaldirection as hinted by a small arrow attached with BBC shown in FIG. 1.It is well known that such an arrangement acts positively as acirculator relative to high frequency electromagnetic wave energy,connecting imaginatively and circutechnique, the additional matchingcircuit of parallel resonance type is inserted in the line at aconsiderably remote position from the gyromagnetic members fromconstructual reasons, resulting in a larger size of the circuit. On theother hand, when a series resonance circuit of half wave length type isemployed for the same matching purpose, the resulting circulator willhave a larger overall size as in the case of the parallel resonancecircuit.

The conventional matching technique requires always a considerablelength of the transmission line to utilize for the provision of theresonance circuit, which prevents a smaller size of the circulatorassembly from being realized. In addition, the frequency characteristicof the related line length will generally adversely affect upon thedesirous broader matching effect.

The main object of the present invention is to provide a more compactand efficient circulator assembly having builtin matching means.

Another object is to provide a circulator of the above kind whichembodies therein unique resonance means.

These and further objects, advantages, special features of the inventionwill become more clear as the description proceeds with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a comparative conventional circulator,shown in its essential constituents only;

FIGS. 2-9 are similar views to FIG. 1, of several preferred embodimentsof the invention;

FIG. 10 is an exploded perspective view of a complete circulatorassembly as constructed in accordance with the novel teaching of thepresent invention;

FIG. 11 is a substantially half of a longitudinal section of theassembly shown in FIG. 0, being taken along a, plane XI-Xl in the samefigure;

FIG. 12 is a comparative diagram of frequency-responsible admittancecharacteristics of specific embodiments according to conventional artand the present invention; and

FIG. 13 is a comparative diagram of operating characteristics ofspecific embodiments of the both kinds above referred to. I

Now referring to FIG. 1, a preferred comparative conventional circulatorassembly will preliminarily described.

larly the extreme terminal ends, as denoted by l, 2 and 3, respectively,of the arms of the conductor, for instance, in the order of 1- 2- 3- I.If assuming the mean or central value of working frequency band of thisconventional circulator be denoted by as conventionally, the band widthwill be f}, :L 10 percent at the highest, under such assumption that thedecoupling amounts to higher than 20 db. As will be well understood, theworking frequency band of this conventional kind of circulator isconsiderably narrow.

An example of frequency characteristic of admittance in a neighboringzone of the working mean frequency f, of the above mentioned circulator,taking as the reference plane a certain plane existing in a closeproximity of the ferrite is shown by a curve A in a Smith chartillustrated in FIG. 12. From this curve, any person skilled in the artwill easily conceive that this circulator is in its equivalency a kindof nonreciprocal resonance circuit. It can be further conceived that inorder to realize a still broadened operating frequency band for thiscirculator it is necessary to provide an additional resonance circuithaving a substantially same loaded Q as that of the characteristic curveA and at a predetermined distance measured outwardly of the circulatorper se from the reference plane for the curve A" and equal to an oddmultiple of quarter wavelength. When adopted such a conventionalmeasure, the circulator will become considerably large in its size andprovide nevertheless only a minor improvement in its broad bandcharacteristic, thus representing a substantial drawback in thepractical view point.

In a first embodiment of the present invention shown in FIG. 2, an innerconductor 14 of the strip line is formed equally as before in the formof three an-n type, having at their free ends terminals denoted equallywith numerals l, 2 and 3. Ferrite discs 12 and 13 are provided similarlyas before. In this embodiment, a round end, radial strip projection 15is formed at the junction of two neighboring side edges of each two armsof conductor 14 and integral therewith. Vertical permanent magneticfield attached equally as before with reference symbols HDC is impressedupon these projections 15. As ascer tained by experiments, projections15 in combination with ferrite discs 12 and 13 forms in effect aresonance circuit, thereby providing by way of example an operatingfrequency characteristic curve denoted by B in FIG. 12. Thischaracteristic depends naturally upon working frequency, the sizes andconfiguration of each projection 15, the kind and nature of ferriteemployed for the projection, and other parameters as will be describedagain hereinbelow. As will be clearly understood from characteristiccurve B," the frequency characteristic of admittance with use of thepresent circulator assembly is considerably smaller than that obtainablewith use of a comparative conventional arrangement as shown by way ofexample in FIG. 1, thus providing a strip-line branching circulatorhaving a considerably broader frequency band.

Determination of the sizes and configuration of radial projections l5relying upon sizes and materials of ferrite discs 12 and 13, thickness,width and the like dimensional data of inner conductor I4, the meanworking frequency and the like parameters may be determined ,bypractical experiments assisted by conventional calculating formulaecommonly known to those skilled in the art.

FIGS. 37, except FIG. 5, illustrate several further preferred andmodified circulator assemblies according to this invention from thatshown in FIG. 1. More specifically, the modified arrangement shown inFIG. 3 differs from the foregoing embodiment inthat each of radialprojections a has a general form of rectangular with straight lineextremity, instead of being formed with rounded end.

In the modification shown in FIG. 4, the extreme end of each radialprojections 15b is pointed. In FIG. 5, the arrangement shown in FIG. 2is illustrated in its top plan view for the purpose of comparison.

In the modified embodiment shown in FIG. 6, each of radial projections150 is formed into a pointed triangle. Each projection 15d shown in FIG.7 is shaped into a rounded triangle.

In all of the foregoing embodiments, radial projections are formedintegral with the strip conductor. In a still further modifiedarrangement shown in FIG. 8, three radial projections 18 are united intoa second and separate conductor 17. This conductor 17 may be placed onthe first conductor fitted with reference numeral 16 in direct physicalcontact therewith, for allowing DC current to be conductive between theboth conductors. Or alternatively, the second conductor is positioned onthe first one through the intermediary of a thin insulator strip,although not shown, for the interruption of DC current conduction. Inthe drawing, the second conductor is arranged symmetrically with thefirst conductor with one and the same center when seen in the top planview. When necessary, however, the both conductors may be arranged in aoffcenter position with each other. Further, as hinted by doubleheadedsmall arrows, the second conductor may be slightly rotated from theposition shown and relatively to the first conductor. By adopting anyone of said measures, or any combination thereof, occasional minorimbalance of admittances at the terminals 1, 2 and 3 may be compensated.Or conversely, these measures may be utilized for intentionally creatingsuch differences as above mentioned, when occasion desires.

In place of several foregoing Y-circulators shown in FIGS. 2-7, aT-circulator is shown in FIG. 9. In this modified arrangement, threeradial projections 20, 21 and 22 are provided, for inner strip conductor19 the first one 20 of which is considerably larger in its size orcovering area than the second and third one 21 and 22. These projectionsare made integral with said conductor 19 as before. In this way, aconsiderably broader frequency band can be realized from the similarreasons as set forth in connectionwith V-circulators.

In the foregoing, inside key constituents of the circulator have beenshown and described with reference to several preferred embodiments.These constituents are contained in a casing 23, preferably circular asshown in FIGS. 10 and 11. The outward extremities l, 2 and 3 of theinner conductor is placed along the central axes of corresponding screwsockets 24 which are fixedly mounted on the outer periphery of thecasing 23 having a closing bottom wall 230. Said sockets are ready forreceiving screw connectors (not shown), respectively, so as to establisheach a conductive connection with a related coaxial line for receptionand delivery of microwave energy, as conventionally. The casing 23 incombination with inside and outside covers 25 and 26, when assembledtogether as shown in FIG. 1 1, acts as outer conductor for thestrip-line. In order to minimize possible transmission losses, thesemembers 23, 25 and 26 are coated galvanizingly with a thin silver layer.Bottom wall 23a and substantial part of the circular casing wall 23,with exception of mounts 24a for connector sockets 24, are made frommagnetic material such as iron, nickel or the like, so as to form amagnetic circuit for permanent magnet 27 in combination with outer cover26 which is made also from a magnetic material. The permanent magnet isso energized that its magnetic field within the interior of thecirculator is transversal to the propagating plane of microwaves to betransmitted.

Gyromagnetic members shaped preferably into ferrite discs 12 and 13 arearranged concentrically with the center of the circulator and stuck onto the respective surfaces of the inner conductor. If necessary,however, these discs may be mounted in position through the intermediaryof a thin insulating layer made from a high dielectric material with lowhigh frequency loss, such as Teflon (trade-mark for tetrafluoroethyleneresin). In addition to one permanent magnet disc as at 27, a similarmagnet may be provided on the lower surface of bottom wall 23a, althoughnot shown. Inside cover 25 may preferably made of an efficientconductive material such as copper.

Characteristic curves A" and B shown in FIG. 12 have been obtained fromtest results with the following dimensional and operating particulars(refer to also FIGS. 2, 5, 10 and l l Corresponding dimensions of thecomparative conventional circulator are just same as those of the novelone set forth hereinbelow:

d3 38 mm., h4= 3.4 mm. (FIG. 2);

w2=2 mm.,l4=7 mm. (FIG. 5);

d1 74 mm., d2= 53 mm. (FIG. 10).

As gyromagnetic material, a material called YIG" (yttriumiron-garnet)was employed which has the following charac teristic properties:

magnetization 471-Ms l4; gausses at 20 oersteds of magnetic fieldstrength;

dielectric constant e 14;

dielectric loss tangent tan 8 3x I 0- Curie point Tc= 190C.

Intensity of permanent magnetic field was 600 gausses as employedthroughout the experiment.

In FIG. 13, several comparative characteristic curves for decouplingamounts, insertion loss, voltage standing wave ratio, and ratio ofworking frequency to mean frequency are shown by way of example.

These curves were plotted upon several experiments carried out under thesame conditions as those employed hereinbefore. Curves Al, A2 and A3were obtained with use of the conventional circulator, while those of"81," 82" and B3 were plotted from the results with the novelarrangement.

The novel circulator assembly can be effectively utilized as branchingorgans as provided along microwave transmission line, for instance,duplexer for microwave transmitter-receiver unit; tunnel diodeamplifier, parametric amplifier or the like.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

1. In a strip-line microwave circulator comprising at least threecentral strip conductors disposed between parallel outer conductors andconnected at one of their ends at a central point with said stripconductors, being parallel to said outer conductors and extendingradially outwardly from said point, including predetermined angles witheach other, a pair of concentric gyromagnetic discs disposed at saidpoint each between one side of said strip conductors and the adjacentouter conductors, and means to magnetize said discs in a directionsubstantially at right angle to said conductors, to create microwavecirculators switching action; the improvement consisting in theprovision of unitary stub conductors disposed between any two adjacentones of said strip conductors, each of said stub conductors having oneend coupled with the junction between the respective strip conductorsand extending outwardly along the symmetry line thereof to a distancebeing in excess of half the radius and less than the full radius of saiddiscs, said strip conductors being in the form of an integral Y-shapedconducting spider strip with the axes thereof including equal angles ofbetween them, said stubs consisting of a further spider strip concentricwith and overlying said first spider strip and movable in aparallelplane relative to the latter so as to compensate for any minor imbalanceof admittances at the input terminals of the circulator, said outerconductors comprising a first cover member and a bottom member extendingover the respective ferrite discs, a casing ring connecting the firstcover member to the bottom member, said means to magnetize said discsconsisting of a single permanent magnet extending over said first covermember, a second cover member extending over said per-

1. In a strip-line microwave circulator comprising at least threecentral strip conductors disposed between parallel outer conductors andconnected at one of their ends at a central point with said stripconductors, being parallel to said outer conductors and extendingradially outwardly from said point, including predetermined angles witheach other, a pair of concentric gyromagnetic discs disposed at saidpoint each between one side of said strip conductors and the adjacentouter conductors, and means to magnetize said discs in a directionsubstantially at right angle to said conductors, to create microwavecirculators switching action; the improvement consisting in theprovision of unitary stub conductors disposed between any two adjacentones of said strip conductors, each of said stub conductors having oneend coupled with the junction between the respective strip conductorsand extending outwardly along the symmetry line thereof to a distancebeing in excess of half the radius and less than the full radius of saiddiscs, said strip conductors being in the form of an integral Y-shapedconducting spider strip with the axes thereof including equal angles of120* between them, said stubs consisting of a further spider stripconcentric with and overlying said first spider strip and movable in aparallel plane relative to the latter so as to compensate for any minorimbalance of admittances at the input terminals of the circulator, saidouter conductors comprising a first cover member and a bottom memberextending over the respective ferritE discs, a casing ring connectingthe first cover member to the bottom member, said means to magnetizesaid discs consisting of a single permanent magnet extending over saidfirst cover member, a second cover member extending over said permanentmagnet, the first and second cover members, a substantial portion of thecasing ring and the bottom member being formed of magnetic material toprovide a magnetic circuit for said permanent magnet.
 2. In a microwavecirculator switch as claimed in claim 1, both said spider strips beingconnected in conductive contact with one another.